Cutting tools cut selected material from workpieces during machining operations. Examples of cutting tools include twist drills, router bits, reamers, broaches, end bores, counter bores, milling cutters and end mills. Cutting tools may cut any material including metal, wood, stone, plastic, composites, fiberglass, and the like.
Cutting tools have a tool body having a mounting portion for mounting in a machine tool and a cutting portion. The cutting portion typically includes cutters away from the mounting portion. Cutters have exposed cutting edges at their outer edges. Moving the tool body forces the cutting edges into the workpiece, cutting away material and removing the cut material from the workpiece.
A cutting tool operates under extreme conditions. Large forces and high pressures are generated during cutting. The cutting edges often become red-hot. Cutting tools may be sprayed with liquids for cooling or to aid cutting. The workpiece may be made from a hard or highly abrasive material that rapidly dulls the tool's cutting edges.
Cutting tools must be both hard and tough. Cutting edges should be as hard as possible to cut into the workpiece and resist dulling. The cutting edges should also be heat resistant to maintain cutting ability and not wear excessively at high temperature. Yet the tool body needs to be rigid and tough. To assure accurate cuts, the tool body must not excessively bend or flex during machining. The tool mounting portion must be sufficiently tough to be held by a machine tool and to resist breakage. If the tool breaks an expensive workpiece may be destroyed, production time is wasted, and operator safety may be at risk.
Cutting tools are conventionally made from tool steel or high speed steel bodies. Special alloy steels are used. The steel is sufficiently hard to form effective cutting edges, yet is sufficiently tough to be held by the machine tool and not break during cutting. The maximum hardness of steel cutting tools is limited. Increasing the hardness of the steel makes the steel more brittle and reduces toughness. The hardness of the steel cutting edges is limited because the steel tool body must not crack or break.
To overcome the compromise between hardness and toughness necessary with steel cutting tools, composite cutting tools have been developed. These include a tool body with cutters fixed to the tool body. The cutting edges of the tool are formed on the cutters. The cutters are made from a hard, temperature-resistant material and the tool body is made from a tough, and less expensive low carbon steel. A composite cutting tool may include a tough, durable tool body carrying hard, temperature-resistant cutters. Composite cutting tools can cut through harder materials more quickly and for a longer time without dulling than non-composite steel cutting tools.
One known composite cutting tool includes a steel tool body with a hard plated coating. The coating usually covers the entire cutting edge portion of the tool. Another known composite cutting tool includes cutters made with hard inserts brazed or mechanically fastened to a steel tool body. The inserts are sharpened to form the cutting edges.
Known composite cutting tools have disadvantages. Plated tools have very thin coatings. The coating usually ranges from two ten thousandths of an inch (0.0002 inch) to five thousandths of an inch thick (0.005 inch). The coating is so thin that pregrinding removes the plating so the tool cannot be resharpened. The entire cutter area is plated, wasting expensive plating material. Brazing or mechanical fastening of cutters to the tool body is time consuming, labor intensive, and requires expensive machining of the tool body. The brazed joint between the cutter and the tool body is prone to fail during cutting, destroying the tool, potentially destroying the workpiece along with it, and risking operator injury.
Thus, there is a need for an improved cutting tool. The cutters should be bonded securely to the tool body, and be sufficiently thick to allow the cutting edges to be finished ground when manufactured and to be resharpened. The tool body should be made from relatively inexpensive but tough metal which can be reliably held by a machine tool and does not crack or break during use.